Making open pits safer, by design

By
Tony Heselev
11 June 2014

Editorial

When CSIRO senior manager Dr. John
Read brought together a group of industry contacts at a conference in Santiago
in 2004 to sound out the idea of pooling knowledge of open pit mine stability,
he was pleasantly surprised with the reaction.

The contacts, representing major mining houses, backed
his idea, providing the genesis for what is now known as the large open pit
mine slope stability project.

Read could not have dreamed that it would have
been so successful however, setting industry standards for reliable large open
pit mine design around the world.

"There was immediate support from
the group for a shared and better understanding of the geological interactions
associated with rock mass failure and recognition of the need for new guidelines
for reliable slope design," Read says.

The project has addressed
an industry-wide need to improve understanding of the relationship between the
strength and deformability of rock and the likely mechanisms of failure in
large open pit mines.

It includes innovative geomechanics research, such
as three-dimensional structural modelling, and is helping mine managers
minimise the risk of loss of life, equipment damage and sustained production
losses in the event of slope failure.

The project is
coordinated by CSIRO and sponsored by 12 mining companies
representing most of the world’s base metals and diamond producers.

By
the end of this year, CSIRO and its partners will have produced four books to
guide professionals such as geotechnical, mining and civil engineers and hydrogeologists
in the investigation, design and construction of stable rock slopes.

Chapters
are written by the people regarded as having the most expertise in each area –
often from the sponsor companies.

The
first book,Guidelines for Open Pit Slope Design (2009), links project research with best practice in open
pit data collection and management; slope design, management and monitoring; and
mining and risk management.

"The book outlines how you collect reliable data,
prepare a geotechnical model, use data for stability analysis, apply that in
mine development and monitor the performance of the mine slopes," Read says.

"Failures will always happen, but what we’re trying
to do is help manage the risk and diminish the likelihood of having a major
failure.

"Companies can do this by having better design and
monitoring practices to keep an eye on what’s going on, especially with slope
management and the development of pore water pressure within the rock mass."

The sponsor companies each provided $100 000 a year
for the research, publishing and project coordination.

Dr
Marc Ruest, De Beers Global Mining’s group lead of geotechnical and hydrogeology,
says the project has been a long-term
commitment that has been extraordinarily collaborative.

"De
Beers has benefited significantly from the large open pit project in so many
ways. CSIRO has effectively brought together engineers from mining houses
around the world to develop a common ground in the critical geotechnical design
and implementation issues at our mine," he said.

"The
guidelines developed as part of the project continue to provide our
practitioners with a high-quality baseline for the geotechnical programs at our
operations."

Dr Read says the guidelines have helped mine
managers become more aware of the need for reliable data and how to assess that
data.

It has also improved their understanding and
assessment of rock mass strength and how to use that information to better
analyse rock stability. This has helped them maximise safety, ore recovery and
financial returns over the life of the mine.

"Risk management is a serious part of the business
these days," Read says.

"Companies make huge investments in these mines and
the mines are also huge.

"Some of the pits are up to 1000 metres deep, for
example Chuquicamata in Chile, and some of the walls will be up to 1400 metres
high, such as at Pelambres, also in Chile."

The book is widely used in Australia, South Africa,
North and South America.

"You can find it on the desks of the geotechnical
people at pretty much every minesite you care to go and visit," Read said.

A second book, on open pit design
and water, was published early this year, expanding on a chapter in the
original guidelines.

Read says this book provides mine
managers with improved information on assessment and monitoring of pore water pressure
in closely jointed rock, and how to incorporate this information into stability
analyses.

A third book, Guidelines for Open Pit Design in Weak
Rocks, and a fourth, Geotechnical
Guidelines for Mine Waste Dump and Stockpile Design, will be released later
this year.

This article originally appeared in full in the CSIRO's Resourceful magazine.

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